Frequency band and channel selecting mechanism



Dec. 30, 1952 J. YAVITCH FREQUENCY BAND AND CHANNEL SELECTING MECHANISM 3 Sheets-Sheet 1 Filed Dec.

INVENTOR JAEUBYAVITEH AT ORNEY v cx INVENTOR JAEUB YAVII :z-z

ATTORNEY 5 Sheets-Sheet 2 J YAVlTCH FREQUENCY BAND AND CHANNEL SELECTING MECHANISM Filed Dec. 29, 1948 Dgc. 30, 1952 l VENTOR UBfl WITEH Zing ATTORNEY 3 Sheets-Sheet 3 RR Q Q36 H u o JAE Dec. 30, 1952 .1 YAVITCH FREQUENCY BAND AND CHANNEL SELECTING MECHANISM Filed Dec. 29, 1948 Patented Dec. 30, 1952 FREQUENCY BAND AND CHANNEL SELECTING MECHANISM Jacob Yavitch, Glenolden, Pa., assignor to Radio Corporation of America, a corporation of Delaware Application December 29, 1948, Serial No. 68,025

18 Claims. (01. 7410.1)

This invention relates to a new and useful channel and band selector mechanism which" is particularly adapted for the selective control of radio apparatus, although not specifically limited thereto.

An object of this invention is to provide a novel selector mechanism wherein a single control member simultaneously moves a plurality of selective switches.

Another object of this invention is to provide a control device for operating a group of switches from a single control member, one group of switches being that of a band switch which also is coupled to vary an antenna switch and another group being that of a channel switch. The band switch selector mechanism is provided with an adjustable cam mechanism and the channel switch is provided with two switches for selectively placing in circuit a predetermined group of capacitors or other tuning elements.

Still another object of this invention is to provide an improved selective mechanism having a variable rotatable cam which permits change in a setting for different bands and which simultaneously operates an antenna tuning switch.

A feature of this invention is the arrangement of three different control units for selective switching. All the control units are simultaneously selected by the movement of a single control knob.

This invention will be more clearly understood by referring to the accompanying drawing wherein:

Fig. l is a plan view of the selector mechanism of this invention;

Fig. 2 is a front elevation, partly in section, of Fig. 1;

Fig. 3 is a rear elevation;

Fig. 4 is a diagrammatic showing of the ear.

train for the channel selector mechanism;

Fig. 5 is a diagrammatic showing of the band selector mechanism; and

'Fig. 6 is an electrical circuit diagram of the channel and band switching circuit including the antenna selective switch.

Referring now in detail to Figs, 1, 2, and 4 of the drawing, an operating knob I is secured to a shaft 2 which shaft is journaled for rotation in a front support casting I24. A spur gear 58 is fastened for rotation on shaft 2 and meshes with another spur gear 56. Also secured to shaft 2 is a stop pin 84, the purpose of which will be explained in more detail later. The ratio between spur gears 58 and 56 being that of 11:10 which permits the knob I to rotate 396 for one complete cycle of 2 rotation, that is, from one channel position to the next, and the gear to rotate 360 for one rotation of the knob I. The gear 56 is fastened to rotate with a main operating shaft 3. Also journaled for rotation in a front support casting I24, is the main operating shaft 3 which rotates in the rear support casting I26. The front and rear support castings are spaced in operative position by four groups of spacers I3 and I4 which are secured by means of screws I5. A small pinion ear is mounted for rotation with shaft 3 and is secured to shaft 3 by a pin IS in a shoulder portion located adjacent the rear support casting I26. A large spur gear 14 meshes with pinion gear 80, which large gear 14 is mounted upon an intermediate shaft d, the shaft 4 being journaled for rotation by a suitable bearing in the rear support casting I26. A pinion gear 16 is also secured to the intermediate shaft 4. Another large spur gear 18 is secured to an adjustable cam shaft 5. The shaft 5 is supported for rotation by needle or roller type of bearings located in both the front and rear support castings. Arranged to rotate with spur gear I8 is an adjustable cam drum 92, details of which will be described later. A control knob stop cam I2 is integral with drum 92 and rotates therewith upon movement of shaft 5. The contour of cam 12 is such as to permit nine complete cycles of rotation of knob I and then look the knob I against further rotation in the same direction. A bell crank 86 is pivoted on casting I24 by a pin 6, the short arm of bell crank serving as a cam follower for cam 12. The long arm of bell crank BIB is provided with 2. depending portion 1, which engages the upper portion of a stop member shown as a lever 84 arranged on the shaft 2. As mentioned above, the knob shaft 2 is provided with a spur gear 58 which meshes with another spur gear 55 on the main operating shaft 3, and the stop lever 84 might optionally be on the form of a pin located on the spur gear 58. The shaft 5 extends slightly beyond the rear support casting and is provided with a pinion 68. The pinion 68 meshes with a gear rack 10. The rack 10 forms part of a sliding arm I02 which is provided with a similar gear rack 64 which meshes with a pinion 62 mounted for rotation on the rear support casting I26 by a shaft 8. The rear extensions of shafts 5 and 8 are provided with channel selector switch operating cranks H8 and MI respectively.

The foregoing description is directed primarily to the channel switching mechanism. The band switching mechanism which operates in conjuncaceaces 3 tion with the channel selecting mechanism will now be described in detail by reference to Figs. 1, 2, 3, and 5.

The adjustable cam drum 5'2 has located thereon, ten adjusting screws 9%, which are secured in position 30 apart by means of a slotted retaining clamp ring I28 located within drum 92. The jacks 96 are slotted at 98a to engage the slots in clamp ring I28. Each one of the adjustable jacks Q5 are provided with adjustable bushings I38, which bushings are mounted for radial move-. ment on the adjusting screws 95 and are-prevented from rotation by means of pins I32 secured in drum 92 which engage a slot 535 in the bushings I36. A forked bell crank member 2a is pivoted at 21, the pivot 2i being secured to the front support casting by means of an extension arm 22. A band setting lever '23 is linked to crank 26 by means of a pin 2%. The lever 23 extends away from the adjustable cam 92 and is provided with depending portion 23a having a slot- 25 and a gear rack 2", the rack 2t meshing with a pinion gear 'Z'i which pinion gear is mounted for rotation in both the front and rear support castings on a shaft '26. The band setting lever 23 is always urged in a position such as to rest upon a bushing I36 by means of a helical tension spring 98 and is stopped only by the height of the preset bushing. The spring 93 is secured at one end to extension 22 and at the other end to an adjustable stud member 2'3, which stud ad,- justs the tension on spring 58 by means of a threaded thumb nut 38. Located above and beyond rack 26 there is provided in depending portions 23a, an aperture 3i, in which a stud member 32 slides. The forward end of stud 32 has mounted thereon a detent roller 3%, which roller engages an approximate heart-shaped detent cam 35. Tension on roller 34 is provided by a helical compression spring 36 surrounding stud 32. The tension of spring 3% is varied by means of a bolt 31' which is threaded in bushing 38. A pin shaft 39 retains lever 23 in operative position by passing through slot 25 in the depending portion 23a. Shaft 39 is secured for rotation on ball bearings I39 located in the forked portion of the front casting I235. The forked portion of casting 524 is recessed to provide the proper support for ball bearings I35. The pinion shaft 28 extends beyond the rear support casting I26 and has secured thereto a spur gear I I6 which meshes with a similar gear ii i mounted for rotation on the rear support casting. The gear lie is an idler gear to'make gears i I2 and I I6 rotate in the same direction. The other spur gear H2 meshes with a pinion gear IIE! which is mounted on a shaft Him for rotation on rear support casting E26 and meshes with a quadrant gear I58. The quadrant gear I08 is provided with a rotatable shaft i2 which operates an antenna selective switch 82. The gears H2 and I it each have secured thereto av band switch coupling lever I25 and I212 respectively. An index scale I89 is marked on casting I25 and a pointer [82a is marked on gear H5. to indicate the proper setting height of bushings I30.

Inthe operation of this switch, when the operator moves the knob I and operating shaft 2 from channel position 1 to position 2, for example, the shaft 2 will complete one cycle or 396 for a movement of the spacing between adjacent channel switch contacts and the spacing between the corresponding selective bushings, band and antenna switch contacts. This greater angular movement between the operating shaft 2. and the movement of the switch shafts is because of a gear ratio of 1 to 3 between the gears 83 and I4 and a ratio of 1 to 4 between gears I6 and It thus making a total increased gear ratio of 1 to 12 from shaft 3 to that of shaft 5. As there are only ten channel positions on drum 92 there is a total of 270 of active movement for the switch selective bushings on cam 92. This movement corresponds with a total of nine complete revolutions of shaft 3 and a corresponding active portion of the adjustable bushings of the band switch. The control knob I is permitted to rotate only a total amount of nine successive rotations or cycles of movement in any direction,

that is, control selections are made from channelposition 1 in succession up to channel position 10 and then back to 1. The above channel or dial positions, namely from 1 to 10 inclusive are not shown on the drawing but may be indicated on any suitable index plate such as, for example, an engraved dial placed in front of the panel. The stop cam E2 in cooperation with the bell crank 86 and stop pin 84 prevents more than'nine successive complete rotations of the control knob I and also prevents the operator from going directly from position 10 to position 1 without going back through the dial or channel positions 9, 8, 7, etc. The gearing arrangement for the channel switch between control knob I and the shaft 5 is such that a 1.1 revolution of the control knob will move the channel switch between operating cranks I I8 and MI 30 or to the next channel po-,

sition. When the operator changes the channel switch position, the band switch will move from a homing position to any selective switch position from 4 to 1 depending upon the height of the preset busings I30. For making up the difference between the increased amount of angular movement of knob I and that of the main operating shaft 3 the gears 58 and 56 have a ratio of 11 to 10 which will permit a greater movement for the operating knob than that of the main operating shaft 3. With this gearing arrangement it is possible to evenly divide the index on the dial into ten equal parts for the knob movement of the nine cycles of revolutions. In other words the front operating panel dial can be divided into 36 equal divisions to indicate an equivalent 30 movement between the. centers of the switch contacts so that one cycle of revolution of the control knob I will move the contact arm of the channel switch A, 30 or to the next channel, thus any of the ten channel positions may be selected in succession up to ten and back to one. During the above mentioned movements of shafts 2, 3, and 5, the heart-shaped detent cam 35 also makes one complete revolution, and the roller 34 is moved backward by the maximum height of the cam. The band setting lever 23 is carried by the rack 26 to a homing position, and at this time the helical compression spring 98 is expandeohand the cam continues its rotation. At the time when the pointer on knob I approaches the next channel position, for example, channel 2, the roller 3G will be driven into the low point of the cam 35 by action of spring 36 thus permitting the tension on spring 98 to be released and drive the lever 23 so that the bell crank 20 will rest upon the next adjacent bushing I30. The height of the bushing will determined how far the bell crank '20 is permitted to drop and this height likewise determines the amount of movement for the band switch shaft by'the relative relationship between the pinion gear 21 and the position of rack 26, for example, if as shown in Fig. 2 of the drawing. the bushingheight is low, the band switch will be such as to select band I It is possible, of course, with a device in this invention to skip from band I to band 4 making a total movement of 120 for the band switch at a time when the channel switch moves only and again it is possible to move from position 1 to position 3 or if desired to position 2. In another arrangement, depending upon the setting of the bushings it is possible to move from position 3 to position 2 or any com bination of selections depending upon the height of the bushings.

When the panel control knob I nears the end of its rotation it is held by the detent action of cam roller 34 and spring 36. The switch arm of the band switch B is released when knob I is held by the detent action and is forced back by spring 98 to any of the bands I, 2, 3, or 4 depending upon the predetermined setting of the cam bushings. The arm 23 is pulled back to the homing position by spring 98 beyond band 4. A

Upon release of knob I movement of arm 23 is stopped by the preset height of the bushings or jacks I30 to the respective positions 2, 3, etc. Any band may be selected by setting the height of the bushing I33 above the periphery of the metal drum 92. The height of the bushing deter mines how far the arm 23 can move the band switch through the rack and pinion arrangement or to rotate switch arms I20 and I22 from the homing or (X) position. Thus by having a band setting bushing for each channel position, any band coil and antenna coil tap may be selected for any one of the channel trimmer or tuning capacitor settings.

- In one arrangement of the selector mechanism of this invention which was used with a transmitter-receiver having a frequency range in the order of 1.5 megacycles to 12 megacycles and a selective arrangement of four bands. For example, the first band can be arranged to cover afrequency range from 1.5 to 3 megacycles, the second hand to cover a frequency range from 3 to 6 megacycles, the third band can cover a frequency range from 6 to 9 megacycles, and the fourth band can cover a range from 9 to 12 megacycles. As mentioned above there is also provided with a band switch the position X wherein the band switch is driven to the homing position by the detent cam 35 roller 34 and the spring loading of spring 36. Coupled with the band switch gears is the antenna switch ANT and shaft I2 operated to move simultaneously therewith.

Referring to the circuit diagram Fig. 6, one example of the use of the switch selecting mechanism of this invention is explained in connection with such a transreceiver having four bands wherein the channel switch is divided in two parts comprising switches A and Al. The two sets of switches are provided to make the set more compact. If desired only a single shaft and one switch may be used. The switches comprise a plurality of wafers like that shown as antenna switch 82 in Fig. 3, except that ten contacts are provided. The band switch is also divided in two parts and comprises switches B and BI. Also coupled with the band switches is an antenna switch ANT indicated as 82 in Fig. 3. Associated with the channel switch contacts are trimmer capacitors IC to IIlC inclusive. The band switch has associated therewith, four inductive elements which are connected to the respective contacts of switches 13 and BI. A series capacitor and inductance taps connect to switch ANT the arrangement being such as to short out portions of the inductance. Avariable tuning slug is provided to tune the antenna inductance. A capacitor C connects to one side of the inductive elements of the band switch and to ground. As mentioned above, the band switches B and BI are both driven to the homing position X every time the panel knob I is operated. The arms of switches B and BI are returned by the spring action of spring 98 to any of the four positions depending upon the preset height of the bushing of the adjustable cam 92. The band switches B and BI are coupled to the selector mechanism by means of the coupling levers I29 and I22. The channel switches A and AI are geared directly for rotation with'the front panel knob I and is arranged to rotate one switch position for each 1.1 revolution of the front panel control. The switches A and AI are coupled to the selector mechanism by means of the coupling levers H8 and I which levers are rotated by means of their respective rack and pinion gears. It will be noted that with this arrangement, it is possible to obtain ten different combinations of band and channel selections with a setting for any frequency within the range of the tuning equipment. Other combinations can be obtained by changing the number of switch positions for selecting the channels and bands in which the channels are found. Theoretically the channel switch and the band setting cam may have any number of settings or positions and the band switch and each plunger of the band setting cam may also have any number of settings or positions. Thus the total number of channels available for given apparatus can be expressed as m-Xn where m and n are any integers representing the number of positions to which the band switch and band setting plunger can be set and the number of positions of the channel switch and band setting cam, respectively. The total number of channels to which the apparatus can be preset is, of course, limited to 11. channels. While theoretically any finite number of channels and bands are possible. it will be recognized, of course, that practical limitations of the apparatus will reduce the number greatly. The device of this invention may be used to select switch positions for any typeof electrical equipment other than that described above. I

What I claim as my invention is:

1. A mechanism for positioning a complementarypair of adjustable positioning devices, including a single control member mechanically coupled to said one of said devices to position the same, a member mechanically coupled to said single control member and having a number of adjustable elements thereon for selection by operation of said single control member, and a further member engaging one of said elements selected by said single control member and mechanically coupled to said other of said devices to position the same in accordance with the position of the element selected by said single control member.

2. A mechanism for positioning a complementary pair of adjustable positioning devices, including a single control member mechanically coupled to said one of said devices to position the same, a member mechanically coupled to said single control member and having a number of adjustable elements thereon, a further member engaging one of said elements selected in response to actuation of said control member, said further member being mechanically coupled to said other of said devices selected by said single control member to position said other device, an addiaeeasec.

tional member mechanically coupled to said single control member and said further member to urge said further member and said other of said devices to an initial position during actuation of said single control member, and an. element mechanically coupled to said further member urging said further member and said other of said devices into position in accordance with the position of the element selected by said single control member.

3-. A mechanism for positioning a complemein tary pairof adjustable positioning devices in n combinations of a total of mXn possible combinations, m and n being any integers, one of said devices being adjustable to 11 positions and the other to m positions, including a single controlmember mechanically coupled to said one. of said devices to position. the same, another member mechanically coupled to said single control member and having. n elements each adjustable to m positions, and a further member engaging one of said elements selected in response to actuation of said single control member, said further member being mechanically coupled to said other of said devices to position the same in accordance with the position of said element selected by said single control member.

4.. A mechanism for positioning a complementary pair of adjustable positioning devices in n combinations of a total of 'mXn possible conibinations, m and n being any integers, one of said devices being adjustable to 72 positions and the other'to in positions, including a single control member mechanically coupled to said one of said devices to position the same, another membermechanically coupled to said. single control member: and having n elements each adjustable to m positions, a further member engaging one of said elements as selected in response to actuation of said single control member, said further member being mechanically coupledv to said other of said devices to position the same in accordance. with the. position of said element selected by said single control member, an additional member coupled to said single control member and. said iurther member to urge said further member and said other of said devices to an initial position during actuation of said single control member, and an elementmechanically coupled to said further member urging said further member and said other of said devices into position in accordance with the position of the element selected by said single; control member.

5. A. mechanism for positioning a complementary pair of adjustable positioning devices in n preset combinations of a total of mxn possible combinations, m and n being any integers, wherein one of said devices is adjustable to 12 positions and the other to m positions, including a single control member directly geared to said one of said devices to position the same, another member geared to said Single control member and having n elements each adjustable to mpositions, a further member engaging one of said elements as selected in. accordance with actuation of said single control member, said further member being mechanically coupled to said other of said devices to position the same in accordance with the position of said element. selected by said single control member, an additional member geared to said single control member and, err-- gaging said further member to urge said further member and said. other of said devices'to an initial position during actuation. of. saidv single: control member; and an. element mechanically coupled to said further member'urging said iurther member and said other of said devices into position in accordance with the position of the element selected by said single control member, and a pair of coacting members mechanically coupled to said other member and said single control member to arrest the control of said single control member at the extremities of travel of said other member.

6. A mechanism for selectively positioning. a pair of complementary adjustable devices, including a single control element mechanically coupled to one of said devices to position the same in direct proportion to movement of said control element, a resilient member coupled to the other of said devices and urging the same in one direction of travel of said other device, an adjustable cam member mechanically coupled to said single control element and to said one device to be positioned in synchronism therewith, and a lever coupled to said other device and engaging said adjustable cam member, said lever and said adjustable cam member being arranged to limit travel of said one device in said one direction to effect the desired positioning of said other devicecorresponding to the positioning of. said one device and said adjustable cam member.

7. A mechanism for selectively positioning a pair of complementary adjustable devices, in-

cluding a single control element coupled to one of said devices to position the same in direct proportion to movement of said control element, a resilient member coupled to the. other of said de-- vices and urging the same in one direction of travel of said other device, an adjustable cam member mechanically coupled to said single control element and said one device to be positioned in synchronism therewith, a lever coupled to said other device and engaging said adjustable cam member, said lever and said adjustable cam member being arranged to limit travel of said one device in said one direction to effect the desired positioning of said other device corresponding to the positioning of said one device and said adjustable cam member, and a further member coupled to said control element and said lever to disengage the latter from said. adjustable cam member during actuation. of said control member.

8. A mechanism for positioning two complementary rotatable devices, including a single control shaft, a first shaft adapted to be coupledto one of said rotatable. devices, gearing cou-- pling said single. control shaft and said first shaft, a mechanism arranged on said first shaft to rotate therewith and having a. plurality of adjustable bushings arranged thereon, a bell crank having one arm. thereof, adapted to. engage. one.

of said bushings at a time, a rack coupled to the other arm of, said bell crank, a pinion engaging said rack, a second shaft adapted to be coupled to another of saidv rotatably adjustable devices, a further gearing coupling, said pinion and said second shaft, a cam geared to said single control shaft element, a cam follower afiixed to said rack,

and; engaging said cam to slide. said rackv and to rotate said bell crank to an inactive position during rotation of said control shaft, and a spring urging said bell crank into engagement with said.

bushings to govern travel of said'bell. crank and said rackin accordance with the height setting, of the bushing selected by operation of said single coupled to. one 'of'said: adjustable devices, gears coupling said single control element and said first member, a drum arranged on said first memher to rotate therewith, a plurality of adjustable bushings arranged around the periphery of said drum, each of said bushings having an internally located adjusting member arranged to vary the height of said bushing with respect to the circumferential surface of said drum, a lever arranged to be slidably moved, a cam geared to said single 'control element, a cam follower affixed to said lever and engaging said cam, a rack afiixed to said lever parallel to the direction of sliding movement, a pinion engaging said rack, a second member adapted to be coupled to the other of said adjustable devices, a further gear coupling said pinion and said second member, said cam being arranged to slide said cam follower and said single control shaft and said first shaft, a drum arranged on said first shaft to rotate therewith, a plurality of adjustable bushings arranged around the periphery of said drum, each of said bushings having an internally located screw arranged to vary the height of said bushing with respect to the circumferential surface of said drum, an arm having a slot therein and arranged for reciprocating movement thereof, a cam geared to said single control shaft, a cam follower affixed to said arm and engaging said cam, a rack afiixed to said arm, a pinion engaging said rack, a second shaft adapted to be coupled to the other of said rotatable devices, a. further train of gears coupling said pinion and said second shaft, a spring urging said'arm and said second shaft to an extreme position defined by the limits of said slot, said cam being arranged to move said arm to the opposite extreme position during rotation of said single control shaft, a bell crank coupled to said lever and having a shoe adapted to engage one of said bushings as selected by rotation of said single control shaft, a further spring urging said arm and said bell crank in contact with said bushing selected by rotation of said single control shaft to restrain the return of said arm in accordance with the height setting of the bushing.

11. A mechanism for positioning complementary rotatable devices, including a single control shaft, including a first shaft adapted t be coupled to one of said rotatable devices having a plurality of discrete active positions totalling less than 360 rotation, a train of gears coupling said single control shaft and said first shaft, a drum arranged on said first shaft to rotate therewith, a plurality of adjustable bushings arranged around the periphery of said drum in accordance with the spacing of the positions of said one rotatable device, each of said bushings having an internally arranged screw adapted to, vary the height of said bushing with respect to the circumferential surface of said drum, an arm having a slot therein and arranged for reciprocating movement thereof limited by said slot, a cam geared to said single control shaft, a cam follower affixed to said arm and engaging said cam, a rack affixed to said arm, a pinion engaging said rack, a second shaft adapted to be coupled to another of said rotatable devices, a further train of gears coupling said pinion and said second shaft, a spring urging said arm and said second shaft to an extreme position defined by the limits of said slot, said cam being arranged to move said arm to the opposite extreme position during rotation of said single control shaft, a bell crank coupled to said lever and having a shoe adapted to engage one of said bushings as selected by rotation of said single control shaft, a further spring urging said arm and said bell crank in contact with said bushing selected by rotation of said single control shaft to restrain the return of said arm in accordance with the height setting of the bushing, a further cam arranged to rotate with said drum, a further cam follower engaging said further cam and having a stop element thereon, a stop engaging member on said control shaft, said further cam having a configuration causing said stop element to engage said stop engaging member at either extremity of travel of said drum to prevent further rotation of said control shaft.

12. A mechanism for positioning an adjustable device to a plurality of predetermined positions within a prearranged sector of travel of said device, including a drive shaft, a mechanical coupling between said drive shaft and said adjustable device, a stop member arranged on said drive shaft, a cam mechanically coupled to said adjustable device, and a lever having a nose portion following said cam and a depending portion arranged selectively to engage said stop member, said cam having a configuration causing said lever to engage said stop member to prevent further rotation of said drive shaft in the forward direction at either end of said sector of travel.

'13. A mechanism for positioning an adjustable device to a plurality of predetermined positions, within a prearranged sector of travel of said device, including a drive shaft, a mechanical coupling between said drive shaft and said adjustable device, said mechanical coupling having a ratio at which said drive shaft is rotated one full turn plus the interspacing between adjacent predetermined positions for each change of position of said adjustable device, a stop member arranged on said drive shaft, a cam mechanically coupled coupling between said drive shaft and said adjustable device, a stopmember arranged on said drive shaft, a cam mechanically coupled to said adjustable device, and a lever having a nose portion following said cam and a depending portion arranged selectively to engage said stop member, said cam having a configuration causing lever to engage said stop member to prevent further rotation of said drive shaft in the forward direction at either end of said sector of travel, a detent cam mechanically coupled to said drive shaft, the last said mechanical coupling having the same ratio as the first said mechanical coupling, and a spring loaded detent follower riding said detent cam to indicate proper positioning of said drive shaft.

and a lever having a nose portion following said,

cam and a depending portion arranged selectively to engage said stop member, said cam having a configuration causing said lever to engage said stop member to prevent further rotation of said drive shaft in the forward directionat either end of said sector of travel, a detent cam mechanically coupled to said drive shaft,

the last said mechanical coupling having the same ratio as the first said mechanical coupling,

and a spring loaded detent follower riding said detent cam to indicate proper positioning of said drive shaft.

16.A mechanism for positioning an adjust :able device to a plurality of prearranged positions within a predetermined positioning range, including a drive shaft, an adjustable cam, a mechanical coupling between said drive shaft and said adjustable cam, a cam following lever arranged selectively to engage said adjustable team, a detent cam mechanically coupled to said drive shaft, 2. spring loaded detent follower riding said detent earn, a member having rack and lever portions slidably mounted on said detent follower, a pinion mechanically coupled to said adjustable device and engaging the rack portion of said member, the lever portion of said member being mechanically coupled to said cam following lever, said detent cam being operable in response to rotation of said drive shaft to shift said detent follower and said rack and lever member to disengage said cam following 'lever from said adjustable cam to enable rotation of the latter in response to further rotation of said drive shaft, and said cam following lever being operable to slide said rack and lever .member on said detent follower to position said adjustable device in accordance with the setting of said adjustable cam.

17. A mechanism for positioning an adjustable device to a plurality of prearranged positions within a predetermined positioning range, including a drive shaft, an adjustable cam, a mechanical coupling between said drive shaft and said adjustable cam, a cam following lever arranged selectively to engage said adjustable cam, a detent cam mechanically coupled to said drive shaft, a spring loaded detent follower riding said detent cam, a member having rack and lever portions slidably mounted on said detent follower, a pinion mechanically coupled to said adjustable device and engaging the rack portion of said member, the lever portion of said member being mechanically coupled to said cam following lever, said detent cam being operable in response to rotation of said drive shaft to shift said detent follower and said rack and lever member to disengage said cam followy pending portion arranged selectively to engage said stop member, said cam having a' configuration causing said lever to engage said stop member to prevent further rotation of said drive shaft in the forward direction at either end of said sector of travel.

18. A mechanism for positioning an adjustable device to a plurality of prearranged positions within a predetermined positioning range, including a drive shaft, an adjustable cam, a

mechanical coupling between said drive shaft and said adjustable cam, said mechanical coupling having a ratio at which said drive shaft is rotated one full turn plus the interspacing between adjacent predetermined positions for each change of position of said adjustable device, a cam following lever arranged selectively to engage said adjustable cam, a detent cam mechanically coupled tosaid drive shaft, a spring loaded detent follower riding said detent earn, a member having rack and lever portions slidably mounted on said detent follower, a, pinion mechanically coupled to said adjustable device and engaging the rack portion of said member, the lever portion of said member being mechanically coupled to said cam following lever, said detent cam being operable in response to rotation of said drive shaft to shift said detent follower and said rack and lever member to disengage said cam following lever from saidadjustable cam to enable rotation of the latter in response to further rotation of said drive shaft, said cam following lever being operable to slide said rack and lever member on said detent follower to position said adjustable device in accordance with the setting of said adjustable cam, a stop member arranged on said drive shaft, a cam mechanically coupled to said adjustable device, the last said mechanical 'position following said cam and a depending position arranged selectively to engage said stop member, said cam having a configuration causing said lever to engage said stop member REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,014,821 Gehrkens Jan. 16, 1912 McKenney Aug. 35 1949 

